1EC(4)                      Kernel Interfaces Manual                      EC(4)
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NAME

6       ec - 3Com 10 Mb/s Ethernet interface
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SYNOPSIS

9       /sys/conf/SYSTEM:
10            NEC  ec_controllers # 3Com Ethernet
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DESCRIPTION

13       The  ec interface provides access to a 10 Mb/s Ethernet network through
14       a 3com controller.
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16       The hardware has 32 kilobytes of  dual-ported  memory  on  the  UNIBUS.
17       This memory is used for internal buffering by the board, and the inter‐
18       face code reads the buffer contents directly through the  UNIBUS.   The
19       address of this memory is given in the flags field in the configuration
20       file.  The first interface normally has its memory at Unibus address 0.
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22       Each of the host's network addresses is specified at boot time with  an
23       SIOCSIFADDR  ioctl.   The  ec  interface employs the address resolution
24       protocol described in arp(4P) to dynamically map between  Internet  and
25       Ethernet addresses on the local network.
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27       The interface normally tries to use a ``trailer'' encapsulation to min‐
28       imize copying data on input and output.  The use of trailers is negoti‐
29       ated  with  ARP.   This negotiation may be disabled, on a per-interface
30       basis, by setting the IFF_NOTRAILERS flag with an SIOCSIFFLAGS ioctl.
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32       The interface software implements an exponential backoff algorithm when
33       notified of a collision on the cable.  This algorithm utilizes a 16-bit
34       mask and the VAX-11's interval timer in calculating a series of  random
35       backoff values.  The algorithm is as follows:
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37       1.   Initialize the mask to be all 1's.
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39       2.   If the mask is zero, 16 retries have been made and we give up.
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41       3.   Shift the mask left one bit and formulate a backoff by masking the
42            interval timer with the smaller of the complement of this mask and
43            a  5-bit  mask,  resulting in a pseudo-random number between 0 and
44            31.  This produces the number of slot times to delay, where a slot
45            is 51 microseconds.
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47       4.   Use  the value calculated in step 3 to delay before retransmitting
48            the packet.  The delay is done in a software busy loop.
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DIAGNOSTICS

51       ec%d: send error.  After 16 retransmissions using the exponential back‐
52       off algorithm described above, the packet was dropped.
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54       ec%d:  input  error  (offset=%d).   The  hardware indicated an error in
55       reading a packet off the cable or an illegally sized packet.  The  buf‐
56       fer offset value is printed for debugging purposes.
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58       ec%d:  can't  handle  af%d.   The  interface  was handed a message with
59       addresses formatted in an unsuitable address  family;  the  packet  was
60       dropped.
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SEE ALSO

63       intro(4N), inet(4F), arp(4P)
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BUGS

66       The  hardware is not capable of talking to itself.  The software imple‐
67       ments local sending and broadcast by sending such packets to  the  loop
68       interface.  This is a kludge.
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70       Backoff  delays are done in a software busy loop.  This can degrade the
71       system if the network experiences frequent collisions.
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753rd Berkeley Distribution       August 20, 1987                          EC(4)